1. Field of the Invention
The present invention relates to semiconductor substrates, and more particularly, to low-pressure wire bonding methods and apparatus that reduce the propensity of low-k dielectric materials of mechanical failure due to wire bonding stresses.
2. Description of Related Art
In semiconductor surface mount technology, integrated circuits (ICs) typically have one or more semiconductor-based circuits wired by metal interconnects, which in turn, have terminal inputs and outputs (I/O) to external circuitry. These ICs are often mounted on a mounting area of a lead frame having leads. Each I/O terminal is then connected to a lead by a thin bonding wire, which is typically made of gold or aluminum.
In making interconnections within an IC, each region of the semiconductor is provided with an electrode for connection with the bonding wire for connecting regions of the IC to each other. For those connections having an external lead, a bonding pad or electrode is typically prepared for making the desired interconnection. This is often accomplished by connecting a bonding wire to the electrode or bond pad by means of thermocompression or thermosonic bonding to form a small, rigid ball at the end of the bonding wire. This small ball is then pressed onto the electrode under high temperature while ultrasonically exciting the wire.
These conventional bonding techniques are often dependent upon a variety of processing conditions including, but not limited to, mechanical pressure, temperature, strength of the electrode or bond pad, power level of the added ultrasonic excitation, time, and so forth whereby any of such processing conditions can ultimately lead to semiconductor failure. For example, compression of the small, rigid ball at the end of the bonding wire often leads to structural damage and/or deformation of the substrate being compressed.
In order to address the foregoing problems, techniques have been directed to on-element bonding that includes bonding a thin metal wire via ultrasonic thermocompression. In so doing, an alloy region is formed to constitute a functional element, and then a thin metal wire is ultrasonically thermocompression-bonded to an electrode formed adjacent to such alloy region. However, this method of attaching wire bonding via thermocompression can undesirably result in forces that are capable of causing distortion, stress, and/or cracks in the pad, electrode or underlying substrate.
Further, wherein the substrate being processed includes a low-k dielectric material, it is commonly known that such materials have poor mechanical strength, and as such, are highly susceptible to damage and/or cracking during any conventional wire bonding technique. This is typically a result of the insertion of a wire bond being inserted with an excessive force during the bonding process, which leads to distortion, stress, and/or cracking of the bonding pad or any other underlying substrate material. In turn, any cracks, stresses and/or distortions in the bonding pad or any other underlying layer jeopardize the strength of the resultant bond and/or device reliability.
Since a reduction in the bond pressure during wire bonding would reduce the probability of cracks in the dielectric, and ultimately enhance reliability, a need continues to exist for improved wire bonding techniques for generating strong, reliable wire bonds while requiring less pressure, temperature, and energy than is accustomed in the prior art, and avoiding any distortion, stress, and/or cracking of the bonding pad and/or underlying substrate material.